1. Field of the Invention
The invention relates to an improved cable-connector system, and more particularly to a system comprising: 1) a low cost, high performance, water blocking aluminum cable as described in U.S. utility patent application Ser. No. 10/131,747 filed Apr. 24, 2002 also assigned to Andrew Corporation and hereby incorporated by reference in its entirety, and 2) a low cost, high performance water-blocking connector uniquely configured to mate with such low cost aluminum cable.
As described in detail in the '747 application, no known cable product exists which met all four of the desired foam coaxial cable attributes: 1) low cost comparable to braided cable cost; 2) electrical properties including shielding effectiveness and intermodulation suppression comparable to that of solid tubular shielded cable; 3) mechanical properties, primarily flexibility, comparable to braided cable; and 4) water blockage comparable to annular corrugated cable.
The unique capabilities of the aforesaid cable were achieved by a novel combination of cable materials, manufacturing methods and cable structural configurations. The very low cost of the cable was achieved in part by the use of an outer conductor composed of aluminum or aluminum alloy. The use of aluminum provides enhanced water blockage by permitting the helical outer conductor during formation to be permanently deformed into the foam insulator material, thus eliminating air gaps at the corrugation crests of the cable and providing a moisture seal.
The manufacturing cost of the cable was dramatically reduced in part by using a dual lead helix on the corrugation, permitting the cable line speed to be doubled. One aspect of the present invention is to provide a connector for such a cable which complements the cable by offering low cost of manufacture, excellent electrical performance and moisture blockage, secure cable retention, and superior ease and speed of field installation.
The unique dual lead helical corrugations and aluminum construction of the cable outer conductor presents first-ever challenges to the connector designer. The dual helical corrugation creates two separate and independent helical grooves which must each be sealed to prevent moisture migration. The use of aluminum as the material for the outer conductor, being much softer and more ductile than conventional copper and copper alloys, has to be treated differently in designing a crimp type connector to prevent over deformation of the outer conductor which could degrade electrical performance of the cable.
To better understand the construction of a dual lead helical cable corrugation, reference may be had to FIGS. 12 and 13. A single lead coaxial cable 175 is depicted in FIG. 12. The single lead coaxial cable 175 of FIG. 12 has an inner conductor 220, a dielectric foam insulator 210 that surrounds the inner conductor 220, and an outer conductor 200 surrounding the foam insulator dielectric 210. The outer conductor 200 has single lead corrugations 195 which compress the foam insulator dielectric 210. The single lead coaxial cable 175 may also have a jacket 190 that surrounds the outer conductor 200. The angle 196 is the pitch angle of the outer conductor 200 corrugations.
A dual lead coaxial cable 180 of the type preferred for use in the system of the present invention is depicted in FIG. 13. The dual lead coaxial cable 180 of FIG. 13 also has an inner conductor 220, a foam insulator dielectric 210 that surrounds the inner conductor 220, and an outer conductor 200 surrounding the dielectric 210. The outer conductor 200 may be a thin strip of ductile material with a longitudinal high frequency weld seam. The outer conductor 200 has dual lead corrugations 197 which tightly compress the dielectric 210. The compression of the dielectric 210 substantially eliminates the formation of fluid propagating air gaps and passageways between the outer conductor 200 and the dielectric 210. The dual lead coaxial cable 180 may also have a jacket 190 that surrounds the outer conductor 200. The angle 198 is the pitch angle of the outer conductor dual lead corrugations 197 which is twice the pitch angle of a single lead helical corrugation 196.
It will be understood from FIGS. 12 and 13 that dual lead helical corrugations are in essence two interposed single lead corrugations. As suggested, this creates two separate helical grooves along the cable which must be closed to block invasion and migration of moisture into the connector.
The chief competition for the novel cable-connector system of the present invention is the various braided cable systems. Braided cable suffers from electrical and water blockage performance which is inferior to the low cost corrugated cable described. Further, as will become evident from the ensuing description of the connector of the present invention, braided cable connectors are much more difficult to attach to the cable, requiring elaborate cable preparation in some cases. They are more expensive to manufacture than the present connector as they all require that the connector body provide an inner ferrule against the electrically conductive braid or foil is compressed to retain the connector on the cable. Means for moisture-blocking the connector may be integrated into or separate from the means for compressively securing the connector on the cable.
The connector of the present system, in contrast offers a relatively simple and low cost approach to securely installing the connector on the cable and preventing moisture invasion into the connector and attached cable. As will be described at length below, the connector of the present invention does not require an inner ferrule against which a braid or foil is compressed to hold the connector on the cable. In one embodiment, internal helical grooves formed in the hollow inner connector body of the connector enable the connector to be simply screwed onto mating corrugations of the cable outer conductor until the connector reaches a stop. To prevent the cable from inadvertently unscrewing or backing out, the connector body is crimped down on the corrugated outer conductor. This prevents the cable from rotating while in use or during assembly, solidly locking the connector permanently onto the cable.
In other embodiments, the internal bore of the connector body which receives the corrugated cable body may be ribbed longitudinally or circumferentially, roughened or otherwise perturbed in other ways such that when the connector body is crimped down on the outer conductor of the cable, it cannot unscrew or otherwise back out.
In preferred embodiments, as will be explained, the connector body is provided with radial external ribs which reduce and control the amount of force required to deform the connector body. The crimping of the connector body is accomplished with a conventional crimping tool having a hexagonal clamp opening.
In accordance with a feature of the present invention, because of the use of the connector with a cable having a an outer conductor composed of soft, ductile aluminum or aluminum alloy, the ribs may be varied in length and/or width to define a deformation profile on the connected cable which permanently secures the cable in the connector, but also optimizes electrical performance and moisture blockage.
The connector component of the system will now be described in detail. It should be understood that while the connector is most advantageously used with the described low-cost cable having a dual lead helically corrugated aluminum outer conductor, the connector may be employed also with other corrugated cables.
2. Description of Related Connector Prior Art
Connectors for corrugated outer conductor cable are used throughout the semi-flexible corrugated coaxial cable industry.
Competition within the cable and connector industry has increased the importance of minimizing installation time, required installation tools, and connector manufacturing/materials costs.
Previously, connectors have been designed to attach to coaxial cable using solder, and or mechanical compression. The quality of a solder connection may vary with the training and motivation of the installation personnel. Solder connections are time consuming and require specialized tools, especially during connector installation under field conditions. Mechanical compression connections may require compressive force levels that are excessive for field installation, and or special tooling that may not be portable or commercially practical for field installation use. Mechanical compression designs using wedging members compressed by tightening threads formed on the connector may be prohibitively expensive to manufacture.
The corrugation grooves of helically corrugated coaxial cable may provide a moisture infiltration path(s) into the internal areas of the connector and cable interconnection. The infiltration path(s) may increase the chances for moisture degradation and or damage to the connector, cable, and or the connector and cable interconnection. Previously, O-rings or lip seals between the connector and the cable outer conductor and or jacket have been used to minimize moisture infiltration. O-rings may not fully seat/seal into the bottom of the corrugations and lip seals or O-rings sealing against the jacket may fail over time if the jacket material deforms.
Heat shrink tubing has been used to protect the connector and cable interface area and or increase the rigidity of the connector/cable interconnection. However, the heat shrink tubing may not fully seal against the connector body, increasing the moisture infiltration problems by allowing moisture to infiltrate and then pool under the heat shrink tubing against the outer conductor seal(s), if any.
Therefore, it is an object of the invention to provide a coaxial connector that overcomes deficiencies in the prior art.